The project is concerned with using the stable isotope 15N, to study protein synthesis in vivo. Protein synthesis rates are measured by infusing a 15N labelled amino acid at a continuous rate and then estimating the synthesis rate from the time course of the infusion and the amount of isotope incorporated into protein. Much of the coming year will be spent on methodology. Specifically we are interested in developing simpler methods of estimating fractional protein synthesis rates and of determining the distribution of 15N among the various amino acids after a single isotopically 15N labelled amino acid has been given.